Histologic and ultrastructural features of normal human parietal pericardium

Morphologic studies of normal anterior parietal pericardium from seven patients revealed this tissue to be composed of three layers: (1) the serosa, consisting of a surface layer of mesothelial cells and a narrow submesothellal space, (2) the fibrosa, containing variously oriented layers of collagen fibrils and small elastic fibers, and (3) the epipericardial connective tissue layer, containing mainly large coarse bundles of collagen and forming part of the pericardiosternal ligament. Scanning electron microscopic examination is most useful for study of the surface features of pericardial mesothelial cells, which have single cilia and are covered with microvilli. The latter bear friction and increase the surface area for fluid transport. Junctional complexes between adjacent mesothelial cells consist of desmosomes, which reinforce intercellular adhesion and zonulae occludentes, which form permeability barriers. Actin-like filaments (50 Å in diameter) are present in microvilli and in immediately subjacent regions of the cells; these filaments mediate changes in cell shape. Intermediate filaments (100 Å in diameter) are associated with desmosomes and form bundles in the perinuclear regions; these filaments provide structural support to the cytoplasm.     

Distribution and relationship of precursor Z material to organizing myofibrillar bundles in embryonic rat and hamster ventricular myocytes

Myofibrillogenesis was examined ultra-structurally in ventricular myocytes from initiation of the heartbeat until one day post term. The pattern of development was nearly identical in both rat and hamster. Both free thin (60 to 80 Å) and thick (160 to 180 Å) filaments were observed predominantly in subsarcolemmal regions. Orientation of free myofilaments proceeded only in association with dense, amorphous material located as plaques along the sarcolemma (frequently in association with binding sites) or as isolated sarcoplasmic condensations. This dense material could be extracted along with the Z lines or organized bundles by 3 m-urea and 0.1 to 0.2 m-sodium tetraborate indicating that plaques and condensations were precursor Z substance. These sites are considered organizing centers since the free filaments of more differentiated myocytes inserted into the precursor material of these loci. Insertion of filaments was either perpendicular to the sarcolemma or, more commonly, parallel to it. The resultant association of filaments with organizing centers produced structures resembling half-sarcomeres. Interconnection of the half-sarcomeres is the proposed mechanism whereby primitive, branched myofibrillar bundles characterized by expansive Z lines and loosely aggregated filaments are formed. Z lines narrowed during subsequent differentiation. Concomitantly, myofilaments were brought into closer contact resulting in the appearance of A-1 interfaces. H bands and M lines were not observed until organogenesis was nearly complete. Intercalated disks developed wherever myofilaments inserted perpendicular to sarcolemmal plaques; the lateral (parallel) connection of myofilaments at Z line levels to the sarcolemmal plaques was retained throughout gestation and in postnatal specimens.     

Ultrastructural modifications of nexuses (gap junctions) during early myocardial ischemia

Ultrastructural alterations in the nexuses or gap junctions of ischemic dog myocardium were investigated with transmission electron microscopy combined with the freeze-fracture technique. The anterior descending coronary artery was occluded for either 45 min, 2 h, or for 45 min with 5 min reperfusion. Nexuses remained physically intact in all ischemic myocardial cells studied even in cells where intercalated discs were separated. However, the distances between transverse densities of the nexuses were significantly reduced from 101 Å in the normal non-ischemic to 51 Å in the ischemic cells. Freeze-fractured replicas showed no overall changes in nexuses examined from myocardium ischemic for 45 min. Structural alterations were frequently observed in myocardium ischemic for 2 h but were also present in myocardium ischemic for 45 min which was then reperfused for 5 min. These alterations were comprised of patches free of P fracture face particles. Interparticle distance was significantly reduced from 184 Å in the normal non-ischemic to 130 Å in the ischemic myocardium. The nexal lesions may be involved in electrical or ionic uncoupling of the ischemic myocardial cells.     

Myocardial ultrastructural changes in Kugelberg-Welander syndrome.

Electron microscopical study of a biopsied specimen of myocardium from a patient with the Kugelberg-Welander syndrome revealed myocardial degeneration, including preferential loss of myosin filaments and abnormalities in the Z bands. Leptomeric fibrils were also observed in the cardiac muscle cell; there does not appear to be a previous report of the finding of such fibrils in human myocardium.     

Myocardial ultrastructural changes in Kugelberg-Welander syndrome

Electron microscopical study of a biopsied specimen of myocardium from a patient with the Kugelberg-Welander syndrome revealed myocardial degeneration, including preferential loss of myosin filaments and abnormalities in the Z bands. Leptomeric fibrils were also observed in the cardiac muscle cell; there does not appear to be a previous report of the finding of such fibrils in human myocardium.     

Microtubules and desmin filaments during onset of heart hypertrophy in rat: a double immunoelectron microscope study

The distribution of tubulin and desmin, the constituent proteins of microtubules and intermediate filaments, respectively, were studied in normal and hypertrophied rat myocardium by high-resolution immunofluorescence and immunoelectron microscopy. Cardiac hypertrophy was induced in 25-day-old rats by aortic stenosis. In the normal heart, double immunolabelling of ultrathin frozen sections of papillary muscle using gold-labelled probes for tubulin and desmin showed that microtubules ran primarily in a longitudinal direction through the intermyofibrillar spaces, perpendicularly to the desmin filaments. Microtubules were present near nuclei, mitochondria, and plasma membranes, while desmin filaments formed transverse connections between adjacent Z disks. No tubulin was observed near the intercalated disks, which were rich in desmin filaments. In hypertrophied hearts, myocytes exhibited the typical morphological features of developing hypertrophy. While there was little difference in the distribution of the microtubules around mitochondria and at the plasma membrane, considerable increases were seen near the nuclei and along the myofibrils. Desmin labelling was distributed transversely as in the controls; however, sometimes it was longitudinally oriented either in the intermyofibrillar space linking 2 Z disks out of register or along digitations of the intercalated disks connecting neighboring desmosomes. The unique rearrangement of desmin and tubulin filaments in hypertrophied cardiac myocytes emphasizes their distinct role in myocyte organization. We suggest that, during the development of cardiac hypertrophy, desmin filaments are mainly involved in maintaining the myofibrils in register, whereas the degree of assembly of microtubules is correlated with the rate of protein synthesis and with myofibrillogenesis.     

Histologic and ultrastructural studies on the myocardium in spontaneously diabetic KK mice: A new animal model of cardiomyopathy

The hearts from spontaneously diabetic KK mice and control mice were examined by light and electron microscopy. Myocardial degeneration, myocardial fibrosis and calcium deposits in the myocardium were extensive in KK mice aged 8 weeks. In myocytes of newborn KK mice, an irregular arrangement of myofibrils and poorly formed Z bands were found. Ultrastructural changes in myocytes of KK mice aged 4 weeks consisted of destruction of mitochondria, degenerated myofibrils and abnormalities of Z bands. However, increased mucopolysaccharides in interstitium and thickened basement membranes of capillaries were not found in KK mice, in contrast to the previous reports of myocardial changes in diabetic C57BL/KsJ mice, alloxan-diabetic dogs and hypertensive-diabetic rats. These observations suggest that the cardiomyopathy found in KK mice is not secondary to diabetes mellitus but is caused by other factors.In conclusion, myocardial ultrastructural abnormalities are present in newborn KK mice. Thus, this animal can be used as a model of cardiomyopathy.     

Three-dimensional immunogold localization of alpha-actinin within the cytoskeletal networks of cultured cardiac muscle and nonmuscle cells.

The ultrastructural distribution of alpha-actinin was studied in cultured hamster heart cells by immunogold replica electron microscopy. This technique enabled us to localize alpha-actinin within the cytoskeletal networks at high resolution and in three dimensions. Colloidal gold, indicating the presence of alpha-actinin, was localized on the Z bands of nascent myofibrils in myocytes and on stress fiber bundles in nonmuscle cells. alpha-Actinin staining was also seen on stellate foci, where cytoskeletal filaments converged along the inner myocyte cell membranes. Intermediate filaments were associated with Z bands of myofibrils, stress fibers, and subplasmalemmal actin networks at the specific points where alpha-actinin was localized on these structures. Heavy meromyosin treatment prior to immunostaining confirmed that the thin filaments contained actin. These results suggest that alpha-actinin serves to interlink these various cytoskeletal elements. In addition, this protein may be involved in the initial phases of filament organization during myofibrillogenesis along the inner surface of the myocyte plasma membrane.     

An ultrastructural study of calcium induced degenerative changes in dissociated heart cells

Dissociated myocytes were prepared by enzymatic perfusion of adult rabbit hearts, and fixed following exposure to various concentrations of Ca²⁺. Only slight ultrastructural changes were noted in myocytes which were maintained in relaxation [(Ca²⁺) < 0.1 μm] or in cyclic contractile activity [(Ca²⁺) ? 0.4 μm]. In these cells, slight swelling permitted clear demonstration of interesting ultrastructural details such as tight connections between Z bands and sarcolemma, attachment of filaments to these structures, and relationships of sarcoplasmic reticulum and T tubules.When the Ca²⁺ concentration was raised above 1.0 μm, sarcomeres exhibited extreme and irreversible shortening, followed by myofilament disorganization, disappearance of Z lines, aggregation of most thick and some thin filaments forming a central mass, and outward displacement of organelles. Under these conditions numerous filaments were attached randomly to the sarcolemma and to intracellular membranes, demonstrating their inherent capacity to bind to membranous structures.The ultrastructural alterations observed in our experiments are similar to those described for the “calcium paradox”, which is likely to be a common pathogenic mechanism of myocardial cell damage.     

Impaired collateral blood flow reserve early after nontransmural myocardial infarction in conscious dogs

The purpose of this study was to determine the adequacy of collateral blood flow reserve of surviving myocardium 3 to 4 days after coronary occlusion in dogs. The proximal circumflex coronary artery was occluded in 9 conscious dogs, and in 7 of these the mid-left anterior descending coronary artery was also occluded. Three to 4 days after myocardial infarction, studies were performed under control conditions and during right ventricular pacing at the maximal heart rate that did not decrease aortic pressure.Pacing increased the heart rate from 110 to 222 beats/min, caused no change in mean aortic pressure (112 to 118 mm Hg), and increased left atrial pressure marginally (13.5 to 16.0 mm Hg) (0.05 <p <0.10). The ischemic zone mass that was dependent on collateral flow because of coronary occlusion was 56% (range 29 to 69) of the mass of the left ventricle, and the mass of the infarct occupied 21 % (range 4 to 41) of the mass of the left ventricle. Subendocardial and mid-myocardial ischemic zone samples contained infarcted tissue and had low control values of coronary vascular conductance (flow/100 mm Hg mean aortic pressure) which tended to decrease during pacing: subendocardium, 0.18 to 0.02 ml · min^?1 · g^?1/100 mm Hg (0.05 <p <0.11), and mid-myocardium, 0.38 to 0.11 (p <0.05). Coronary vascular conductance in normal zone subepicardium increased 35% from control conditions to pacing (1.24 to 1.69 ml · min^?1 · g^?1/100 mm Hg; p <0.03). In contrast, coronary vascular conductance in surviving myocardium located in the subepicardial layer of the ischemic zone did not change during pacing (1.17 to 1.21 ml · min^?1 · g^?1/100 mm Hg).It is concluded that collateral blood flow in surviving myocardium within the initial zone of ischemia returns to normal under control conditions by 3 to 4 days after coronary occlusion, but there is no reserve capacity to increase collateral conductance. Impaired collateral reserve in this unique canine model is probably related to multivessel occlusion and to the short period of time collateral vessels had to develop (3 to 4 days after coronary occlusion). If these findings are clinically applicable, they suggest that severe stress after acute myocardial infarction has the potential to provoke ischemia and its consequences in the surviving tissue supplied by occluded coronary arteries.     

Biochemical and ultrastructural changes in skeletal muscle induced by a creatine antagonist

To evaluate the essentiality of creatine and phosphocreatine for the maintenance of the ultrastructure of skeletal muscle, chicks were fed a creatine antagonist, β-guanidinobutyric acid (β-GBA), as 2% of a Chow diet. Chicks fed β-GBA exhibited growth retardation and weakness, and they accumulated large amounts of a monosubstituted guanidino compound, presumably β-GBA, in their skeletal muscles. After 2 wk, there was a 74% decrease in the uptake of [¹⁴C]-1-creatine into pectoralis muscles of chicks fed β-GBA. After 3 wk there was a significant decrease in phosphocreatine concentrations in pectoralis muscles from 20.1 ± 2.8 μmoles per g wet weight (mean ± S.D.) for 8 control chicks to 16.5 ± 2.5 for 7 chicks fed β-GBA. Selected fibers of the pectoralis and gastrocnemius muscles of chicks fed β-GBA exhibited ultrastructural abnormalities including loss of thick and thin filaments, disruption of the Z band, dilated mitochondria, and dilated and displaced sarcoplasmic reticulum. The pectoralis muscles of chicks given 6% creatine in addition to 2% β-GBA in the diet accumulated little β-GBA, maintained normal phosphocreatine concentrations, and exhibited no significant ultrastructural abnormalities. These findings are the first experimental evidence that high concentrations of phosphocreatine are essential for the maintenance of the ultrastructural integrity of skeletal muscle.     

The effect of noradrenaline on blood flow and oxygen consumption in normal and ischemic areas of myocardium

The effects of infusions of noradrenaline (1.0 μg/Kg./min.) were studied in dogs 2 to 3 hr. after acute ligation of the anterior descending branch of the left coronary artery. The model allowed blood flow to be simultaneously measured in the ischemic (infarcting) region and in the normal myocardium. Sampling blood from a local vein (draining the ischemic region) and from the coronary sinus (draining the normal myocardium) allowed comparisons to be made of oxygen consumption by the two regions.Coronary artery ligation resulted in a marked decrease in cardiac output and external cardiac work and an increase in left ventricular end-diastolic pressure with an unchanged LV $\text{dP}\text{dt}$. This is indicative of reduced myocardial contractility. Blood flow in the area supplied by the ligated vessel fell to a mean of 17.6 ± 2.7 ml./100 Gm./min., which is about 20 per cent of the normal flow in this region.Infusing noradrenaline 2 to 3 hr. after ligation increased systemic arterial pressure, LV $\text{dP}\text{dt}$ max, external cardiac work, and blood flow and oxygen consumption in normal areas of the myocardium. There was some evidence that pulmonary shunting was increased by the drug.Noradrenaline also markedly increased peripheral coronary pressure and blood flow in the ischemic region, as assessed by ¹³³Xenon clearance and by retrograde flow from the ligated vessel. Oxygen consumption in the ischemic region was also increased by noradrenaline. It is suggested that part of the increase in flow occurs in the endocardial region since the effective subendocardial perfusion pressure is increased by noradrenaline. This increase in flow would account for the reduction in infarct size which has been observed by other workers when the systemic arterial pressure is raised.     

Morphometry of cardiac hypertrophy induced by experimental renal hypertension.

A method for determining the mean volume of cells within a tissue has been applied to the measurement of endocardial and epicardial myocytes in the left ventricle of normal and hypertensive rats. The technique is based on nuclear counts per unit area in tissue slices of different known thicknesses. It measures the mean cell volume per nucleus and has been combined with electron microscopic morphometry. Compared with the epicardial regions, the normal endocardial regions contained 30 percent more myocytes, 27 percent less interstitial space, 48 percent less capillary volume, 17 percent less capillary surface and the same capillary length per unit of tissue volume. In terms of both the relative and absolute volumes and surface areas of their organelles, the cytoplasmic composition of normal endocardial and epicardial myocytes was nearly identical.After 1 to 4 weeks of hypertension induced by renal arterial constriction, endocardial myocytes enlarged from 10,370 ± 410 to 12,520 ± 490 μ m³ whereas epicardial myocytes enlarged from 12,600 ± 1,600 to 17,300 ± 1, 100 μm³. The number of myocytes and the total length of capillaries remained constant. The epicardial region enlarged 37 percent with proportional increases of myocyte and interstitial volumes. In contrast, the endocardial enlargement was only 26 percent, consisting of 21 percent hypertrophy of myocytes and a 55 percent increase in interstitial components. Expansion of capillary lumens accounted for much of the interstitial enlargement throughout the myocardium. Hypertrophy of myocytes in the epicardial region was accompanied by a reduced mitochondria to myofibril ratio and disproportionately large increases (two- to three-fold) in both smooth endoplasmic reticulum and T system volume and surface area. On a cell basis the morphometric characteristics of myocytes from hypertensive rats are significantly different from normal, and significant differences occur between the inner and outer layers of the myocardium for practically every cytoplasmic component.     

Three-dimensional ultrastructure of normal rat hepatocytes by quick-freezing and deep-etching method

The three-dimensional ultrastructure of nuclei and cell organelles including rough-surfaced endoplasmic reticulum (RER), mitochondria, and cytoskeleton were studied in normal rat hepatocytes by the quick-freezing and deep-etching method. Peroxisomes and mitochondria were observed as spherical structures with granular matrices. Peroxisomes were identified by their size and matrices, which were more condensed than those of mitochondria. Ribosomes were identified as granular structures and were attached to the surface of endoplasmic reticulum. Cytoskeletal filaments were identified by their differences in diameter on the replica membranes, as well as in conventional ultrathin sections. Microfilaments were mainly localized around the bile canaliculi and adjacent to sinusoids. Intermediate filaments were observed around the bile canalicular microfilaments. Only a few filaments were observed near the lateral plasma membranes. Cross-bridges measuring 5-7 nm in diameter were localized between the lamellae of RER and the surface of mitochondria. The quick-freezing and deep-etching method could be used to clarify the three-dimensional association between the cytoskeleton and membrane-bound organelles in hepatocytes.     

Nuclear pores in ventricular muscle cells from adult hypertrophied hearts

Nuclear pores were observed in myocardial cells in both spontaneous and experimentally induced hypertrophy. The ultrastructure of these pores was studied in cross sections and tangential sections of hypertrophied rabbit, hamster and guinea pig heart cells. The morphology was similar to that previously seen in normal cardiac cells and in other cell types. Clusters of nuclear pores were frequently seen, and the closest center-to-center spacing between pores was 1400 Å. Annular granules with associated fibrils were observed on both the cytoplasmic and nucleoplasmic sides of the nuclear envelope. Many of the pores contained granules ～ 300 Å in diameter which sometimes appeared hollow. The presence of large numbers of nuclear pores in hypertrophied cardiac cells supports the hypothesis that transport of material necessary for RNA-mediated protein synthesis may occur through the pores. Furthermore the mature cardiocyte provides an opportunity to study nuclear pore function in nuclei that do not synthesize DNA or divide.     

Metabolism of luteinizing hormone by the pseudopregnant rat ovary

The subcellular localization of myosin in thyroid was investigated by both immunofluorescence and biochemical techniques. Dog thyroid cells stained with antisera to gizzard or thymus myosins showed that epithelial cells from thyroid contain nonmuscle myosin but not smooth muscle myosin. The antimyosin staining appeared at the periphery of the cell and in fibrils within the cell. The nature and subcellular localization of the myosin were further probed using biochemical techniques. Bovine thyroid plasma membranes were isolated by flotation on sucrose density gradients and subsequently extracted with 1% Triton X-100 to prepare an insoluble cytoskeletal fraction. After washing to remove residual Triton X-100, sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the cytoskeletal fraction demonstrated two major bands and several minor bands. The higher molecular weight band of the two major bands comigrated with the 200,000 mol wt heavy chain of myosin. Phosphorylation of the cytoskeletal fraction by thyroid myosin light chain kinase demonstrated a calcium- and calmodulin-dependent phosphorylation of the 20,000 mol wt light chain of myosin. Furthermore, the cytoskeletal fraction contained a myosin-type EDTA-K+ ATPase activity which was not influenced by ouabain and sodium azide. These results demonstrate the association of myosin with thyroid plasma membranes. Little myosin was solubilized by incubation of the thyroid plasma membranes with 0.6 M KCl; however, the addition of 10 mM ATP and 10 mM MgCl2 solubilized most of the myosin, indicating that it is associated with the thyroid plasma membranes through interaction with actin filaments. The presence of myosin in the thyroid plasma membranes may be important in endocytosis and exocytosis involved in thyroid hormone secretion.     

心肌病心肌肌钙蛋白Ⅰ磷酸化及降解的初步研究

目的探讨心肌肌钙蛋白Ⅰ（cTnⅠ）在心室扩张、心力衰竭患者心肌组织中的磷酸化与降解及其信号通路调节。方法4例原发性扩张型心肌病患者。3例其他病因继发心室扩张,心脏移植术受体心脏,1例行双瓣膜置换及左心室改良术,部分左心室切除心肌组织。6例正常心脏。分别行光镜、电镜病理学检测,Western blot方法检测左心室心肌组织cTnⅠ磷酸化、去磷酸化,cTnⅠ降解片段及蛋白激酶C（PKC）表达,甘油醛-3-磷酸脱氢酶（GAPDH）作为内参半定量。结果扩张左心室心肌内均检测到cTnⅠ表达及降解片段,正常左心室心肌内均可见cTnⅠ表达,未见降解条带。扩张左心室心肌均有明显磷酸化cTnⅠ表达,半定量结果均明显高于正常对照组（P〈0．05）,两组心肌病表达比较差异无统计学意义。扩张左心室心肌内均可见程度不同的去磷酸化cTnⅠ表达,正常组未出现明显去磷酸化cTnⅠ表达。扩张左心室及正常对照组左心室心肌组织内均未检测到明显的PKCβ1、PKCβ2表达。结论扩张心室心肌组织内cTnⅠ降解片段的存在可能与心肌病变的发生、发展有关,并在长期慢性心功能的损害中起重要作用。衰竭心肌组织内cTnⅠ磷酸化程度显著增强,PKCβ1、PKCβ2与其磷酸化程度增高可能不相关。     

Tubuloreticular structures in myocardium: An ultrastructural study

Tubuloreticular structures were observed in cardiac tissue obtained either by biopsy or by operative resection in five (3%) of 169 patients with diverse conditions. Two of these five patients had congenital heart disease; one, aortic valvular disease, and two had cardiomyopathy, which was associated with thyrotoxicosis in one patient and with polymyositis and chronic alcoholism in the other. Tubuloreticular structures were composed of curved or undulating tubules that measured from 200 to 300 Å in diameter, branched extensively, and formed net-like masses either within cisterns of endoplasmic reticulum or within the perinuclear cistern. They occurred in endothelial or fibroblast-like cells, but not in cardiac muscle cells. These structures are known to occur in a wide variety of normal and abnormal animal and plant cells. They are formed through a specialized type of deformation of the membranes of the endoplasmic reticulum. Their precise significance is unknown. Criteria are given for the distinction between tubuloreticular structures and other types of morphologically similar structures that have been described in muscle cells, including aggregates of tubules of sarcoplasmic reticulum, tubules derived from the inner nuclear membranes, annulate lamellae, and highly organized arrays of developing T tubules.     

Determination of left ventricular mass by computed tomography

The purpose of this study was to determine the spatial distribution of lidocaine relative to blood flow in ischemic, normal and border zone canine myocardium. Ischemic zone tissue was distinguished from normal zone tissue by a special microsphere technique in adjacent sections 4 to 5 mm wide from the center to the lateral border of the ischemic region in 14 open chest dogs. Gamma-labeled microspheres were separated by a special technique from carbon-14 ([¹⁴C])-lidocaine in the same tissue sample. Blood flow (mean value ± 1 standard deviation) was reduced to 46 ± 25 percent of normal in the ischemic subepicardium and 17 ± 18 percent of normal in the subendocardium. [¹⁴C]-lidocaine was 0.56 ± 0.12 μg/g in normal myocardium 10 minutes after bolus injection of [¹⁴C]-lidocaine; it was reduced to 91 ± 15 percent of normal in ischemic subepicardium and 58 ± 12 percent of normal in the subendocardium. Blood flow and lidocaine concentration were uniformly lowest in gross samples from the central and intermediate ischemic zones, and highest in the gross samples from the border normal zone (p < 0.05). The values for flow and lidocaine in samples from the border ischemic zone were intermediate, that is, higher than values from central ischemic (p < 0.05) and lower than values from border normal zone samples (p < 0.05). However, the labeling technique for normal zone tissue revealed that the values of blood flow and lidocaine in the gross samples from the lateral border of the ischemic zone were intermediate between those of adjacent ischemic and normal samples because of the mixture of overlapping normal and ischemic tissues components—not because of a unique mildly ischemic region. Both blood flow and lidocaine concentration were lower in the subendocardial third than in the subepicardial third of the ischemic zone (p < 0.05) even after the contribution of normal zone tissue was subtracted, suggesting a gradient of ischemia across the transmural border zone.In conclusion, lidocaine is distributed uniformly in ischemic components from the center to the lateral border of the ischemic zone, but there is an endocardial to epicardial gradient. Both lateral and transmural border zone distributions must be considered to understand the mechanisms of drug effects in myocardial ischemia.     

Changes in cardiac ultrastructure and myofibrillar proteins during ischemia in dogs, with special reference to changes in Z lines

This study was designed to examine whether or not coronary ligation produces changes in myofibrillar proteins, especially Z line proteins including alpha-actinin and the 55 kDa protein, in the dog. Changes in ultrastructure of the myocardium after coronary ligation were also studied. A branch of the left anterior descending coronary artery was ligated for a period of 3, 6, 24 or 72 h. Coronary ligation produced ultrastructural changes in Z lines (characterized by broader and wavy Z lines) as well as changes in glycogen granules, mitochondria, and nuclei. Myofibrils were isolated from the myocardium that had been made ischemic by coronary ligation. The yield of myofibrils was reduced as the ischemic period was increased. Phase microscopic examination of the isolated myofibrils from the ischemic myocardium revealed that there were spread Z lines with wider I bands, these changes being essentially the same as those observed by the electron microscope in the ischemic myocardium. The effect of coronary ligation on the myofibrillar proteins was studied by means of polyacrylamide gel electrophoresis. In the isolated myofibrils from the myocardium 3 h after coronary ligation, there were decreases in the percentage of actin, alpha-actinin and the 55 kDa protein, and these changes progressively increased with lengthening of the ischemic period. These results suggest that coronary ligation decreases actin, alpha-actinin and the 55 kDa protein, in association with ultrastructural changes of the Z lines.